The Internet of things (IoT) is the inter-networking of physical devices, vehicles, buildings, and other items embedded with electronics, software, sensors, actuators, and network connectivity that enable these objects to collect and exchange data. IoT is expected to offer advanced connectivity of devices, systems, and services that goes beyond machine-to-machine (M2M) communications and covers a variety of protocols, domains, and applications.
IoT can be encapsulated in a wide variety of devices, such as heart monitoring implants, biochip transponders on farm animals, automobiles with built-in sensors, automation of lighting, heating, ventilation, air conditioning (HVAC) systems, and appliances such as washer/dryers, robotic vacuums, air purifiers, ovens or refrigerators/freezers that use Wi-Fi for remote monitoring. Typically, IoT devices encapsulate wireless sensors or a network of such sensors.
Most IoT devices are wireless devices that collect data and transmit such data to a central controller. There are a few requirements to be met to allow widespread deployment of IoT devices. Such requirements include reliable communication links, low energy consumption, and low maintenance costs.
To this aim, an IoT device and a connected wireless sensor are designed to support low power communication protocols, such as Bluetooth low energy (BLE), LoRa, and the like. However, IoT devices utilizing such protocols require a battery for power, such as a coin battery. The reliance on a battery power source is a limiting factor for electronic devices, due to, among other elements: cost, size, lack of durability to environmental effects, and the requirement for frequent replacement. As an alternative to using batteries, power may be harvested from environmental sources such as light, movement, and radio frequency transmissions. In order to minimize the power consumption, IoT devices are designed with the minimum required components for implementing low-power consumption oscillators.
FIG. 1 schematically illustrates a standard BLE transmitter 100 including a BLE packetizer 110, an oscillator 120, a power source 130, an amplifier 140, and an antenna 150. These components allow for the transmission of wireless signals from the BLE transmitter 100.
The BLE standard defines 40 communication channels from 2.4000 GHz to 2.4835 GHz within the industrial, scientific and medical (ISM) bands. Out of the 40 Bluetooth channels, 37 channels are used for communicating data and the last three channels (channel numbers: 37, 38, and 39) are used as advertising channels to set up connections and send broadcast data. The BLE standard defines a frequency hopping spread spectrum technique in which a radio hops between channels on each connection event. A broadcaster device may advertise on any one of the 3 advertisement channels. The modulation scheme defined for the BLE standard is a Gaussian frequency shift keying (GFSK) modulation. To this end, within each channel, a frequency deviation greater than 185 KHz above the carrier frequency corresponds to a bit with a binary value ‘1’, and a frequency deviation less than 185 KHz corresponds to a bit with a binary value ‘0’.
The BLE packetizer 110 may receive a signal originated from a processor of a host device. Such a signal may include data or control parameters included in the signal transmitted by the BLE transmitter 100.
The oscillator 120 generates a radio frequency (RF) carrier signal that may carry the data signal generated by the BLE packetizer 110. The modulated RF signal, carrying the data signal, is amplified by the amplifier 140 and then broadcast by the antenna 150. The power source 130 may be a battery.
The oscillator 120 may be a free-running oscillator, which may be used to directly generate an RF carrier signal. Thus, a free-running oscillator may replace a frequency synthesizer to generate an RF carrier signal. Utilization of a free-running oscillator may result in power savings. In the BLE transmitter 100, the free-running oscillator generates an RF carrier signal having a frequency within a specific portion of the wireless spectrum, e.g., the 2.4 GHz wireless spectrum.
Typically, the free running oscillator is locked via a phase-locked loop (PLL) to a clock, originating from a crystal oscillator. The crystal oscillator has a resonator 121 that may be also included on a board hosting the processor of an IoT device. The resonator 121 is typically a crystal resonator, e.g., a quartz resonator, or a microelectromechanical systems (MEMS) based resonator which typically provides a sufficiently accurate and stable time/frequency reference. However, for low-cost, low-powered, and small form-factored IoT devices, it is desirable to omit such a resonator.
Some devices, such as radio frequency identification (RFID) devices, use an external signal as a reference signal. Typically, an RFID reader demodulates a received signal onto the carrier wave transmitted to RFID tags. An RFID tag receiving the carrier wave reference signal can synchronize its own transmission based on such a signal. The RFID does not time the transmission, but merely transmits data as the reference signal is received. This synchronization solution cannot work in BLE transmitters where transmission must occur in specific sessions (or time slots).
Therefore, in order to calibrate BLE transmitter using over-the-air signals, it would be advantageous to provide solutions that can detect signals that can be utilized for such calibration.